The events involved in tumor initiation and promotion in mouse skin and liver will be scrutinized. Numerous studies to date have led us to the conclusion that the initiation produced by low doses of polycyclic hydrocarbons in mouse skin differs in degree from that produced in rat liver or bladder. We will undertake to identify the events responsible for this distinction through the use of a mutagenic, chemically active aromatic amine, which does not initiate liver tumors in the Peraino regimen, namely 2-acetamidophenanthrene. Through combination of the limited effect of this compound with the various regimens which have been developed for sequencing hepatocarcinogenesis, we will seek to better identify the roles of these regimens. In mouse skin, we have obtained evidence that the early steps in promotion by 12-0-tetradecanoylphorbol-13-acetate may lead to a differentiation pathway which is resistant to cancer induction. This will be pursued further, along with further experiments designed to show differences between compounds in the ratio of promoting activity to initiating activity. Numerous adducts have been isolated from livers of rats treated with 2-acetamidophenanthrene and 4-acetamidostilbene, but have not been identified. Efforts will be made to identify these adducts, as well as what appears to be a new adduct from acetamidofluorene treatment. Markers will be prepared from the reactions of the appropriate N-acetoxy-N-trifluoroacetyl-N-arylamines (which decompose to yield N-arylnitrenium ions) with nucleosides, and with nucleic acids bearing tritium only on G, C or A. In collaboration with L. Loeb of the University of Washington, defined lesions on templates for DNA polymerase will be prepared and tested for their effects on replication. The polyelectronic perturbation method for determining relative energies for a series of potentially competing reactions will be further developed, using the molecular mechanics program of Allinger to define reaction geometries.